The present invention relates generally to flammable liquid storage tanks, and more particularly, is directed to a manifold fitting suitable for use with tank vapor control systems.
It is common practice to store flammable liquids, such as various petroleum products, in storage tanks which may be located either above ground or below ground. In view of the fire hazard attendant with the storage of such flammable liquids, code officials, insurance underwriters and fire prevention officials have engaged in studies to establish suitable regulations to provide for adequate storage of such materials. As a result of this effort and study, both in this country and abroad, suitable safety standards have been promulgated which provide for storage of flammable liquids, such as gasoline, in underground storage tanks of suitable size and strength for the purpose. The safety regulations provide for such variables as depth of storage, spacing between tanks and flammable vapor venting systems.
It has long been required that all or substantially all flammable liquid storage tanks, either of the above ground type or underground type, be provided with suitable venting devices to equalize pressures within the tank. Most commonly, venting devices have consisted essentially of a vent pipe connected directly to the vapor space within the tank in a manner to lead flammable and other vapors upwardly to atmosphere at some distance above grade level. It has been found that the usual venting systems, as above described, have generally provided adequate safety for the flammable product stored within the above ground or underground storage tanks. Accidents directly attributable to the tank venting systems, when adequately functioning, are extremely rare.
More recently, considerations other than strict vent safety have arisen and now, concerned citizens have become cognizant of the ecological problems arising from flammable liquid storage in relatively crowded areas. It has been found that considerable pollutants can be introduced to the atmosphere through the vent pipe of flammable liquid storage tank unless adequate provisions are made to control the release of such flammable vapors. In accordance with more recent studies made of the venting systems of flammable liquid storage tanks, concern has been directed to the effect of the flammable vapors which have been heretofore freely discharged into the atmosphere through the tank vents. These studies have also concentrated on the environmental changes and effects caused by the release of such vapors and accordingly, the more recent studies have encompassed areas much wider in scope than merely the safety factor consideration of such flammable liquid storage.
As a result of the environmental considerations, the venting systems of flammable liquid storage tanks are now being rapidly changed from the previous simple open vent to atmosphere as heretofore deemed necessary and desirable for purely safety considerations, to some type of normally closed, but openable when necessary, type of storage tank vent system, from the standpoint of air pollution control.
It has been found that most pollutants escape through the vent system during the tank fill operation. Accordingly, systems have been devised wherein the vapors that heretofore were forced upwardly to atmosphere through the tank vent during the tank fill operation are now returned directly to the tank truck through a vapor return system.
Prior workers in the art have encountered difficulties in installation and servicing of such vapor return systems, particularly when converting existing underground tank vent systems to the controlled vapor release or vapor return system. Considerable excavation has been required to expose both the tank fill pipe and the tank vent pipe of each underground storage tank to equip such tanks with a vapor return system. In the case of servicing underground storage tanks that have proved defective for one reason or another, a considerable excavation and servicing has always been required to take corrective action.